Position determination and communication systems have various applications. A preferred embodiment of the present invention would be as a golf course ranging and communication system. Golfers are frequently interested in knowing their distance to the pin or golf course obstacles from the tee or fairway locations. Skilled golfers, and in particular professionals, can control their shots to within a few yards of a desired target. Thus it is of considerable advantage to this class of golfers to be able to estimate their distance to the pin or other locations with very high accuracy from any feasible position of play.
Previous systems have relied on optical sighting systems, dead-reckoning systems, and RF-based systems. For example, in U.S. Pat. No. 3,868,692 issued to Woodward, a transmitter placed at each pin broadcasts a continuous wave RF signal. A hand-held unit measures the field-strength of the signal emitted by each pin and uses an analog meter to indicate yardage to the pin. This system is straightforward and simple, and allows the plurality of hand-held units to operate on a non-interfering basis, but requires the golfer to visually estimate yardage from an analog meter on the handheld unit. Accuracy can also be affected significantly by analog component tolerances and aging, as well as low levels of unexpected RF interference at the transmitter frequencies.
In a system to Henriques and Angleman (U.S. Pat. No. 4,297,701), a hand-held transceiver unit transmits a coded signal to a flagstick-mounted unit, which is itself, a transceiver. The flagstick unit is identified by the code, and the identified flag stick unit re-transmits the received signal back to the hand-held unit. Distance estimation is based on measuring the two-way signal delay between the hand-held and the flagstick units, which is implemented in the hand-held unit by charging and discharging of a capacitor. The system described above also suffer from the necessity to mount the transmitter or transceiver unit on or near the flagstick, where it may be easily damaged and is undesirable aesthetically, or may not be permitted. Another limitation of the system is that the signal transmission between the hand-held unit and the flagstick unit for a reliable distance measurement usually requires the two units to be in line of sight, which is not feasible in some positions within the golf course.
U.S. Pat. No. 4,698,781 issued to Cockerell and U.S. Pat. No. 4,703,444 issued to Storms et al. both describe a system in which hand-held transceiver operate in conjunction with a triangular arrangement of fixed-position transceivers (transmitters) which eliminate the need for flag-pole mounted units. Each hand-held interrogation unit stores the coordinates of key course features and fixed-position transceivers and can provide the golfer with an estimate of his distance to any of these features on a particular hole. In the system to Cockerell, the fixed-position transceivers contain either a clock or an interferometer to measure time of arrival or bearing from the mobile interrogator. The fixed-position transceivers then relay the time-of-arrival and/or bearing information to a central processor. In order to make accurate time-of-arrival measurement, the clocks at the three fixed-position transceivers are required to be synchronized in time such that precise time reference is available. Thus, high precision and stable clocks and constant calibration of the clocks are required. In the system to Storms, et al., three fixed-position transmitters transmit repetitive pulse sequences which are received and processed by the hand-held interrogation unit. The hand-held unit estimates the difference in the arrival time between the pulses transmitted by the first and second transmitters, and then the arrival time difference between the pulses from the second and third transmitters. Based on these two time-difference estimates, the hand-held unit computes it's current location and then computes and displays the distance to the desired course feature. In this system, the fixed-position transmitters need to be synchronized in time. Thus, high precision and stable clocks and constant calibration of the clocks are required.
The spread spectrum ranging and direction-finding system issued to Wang, et al (U.S. Pat. No. 5,056,106) employs four fixed position reference transmitters and a handheld receiver. The handheld receiver measures pseudo-range from the four reference transmitters and performs triangulation to determine its position. A hierarchical master-slave synchronization scheme is used to synchronize the clock of the reference transmitters. This hierarchical master-slave synchronization scheme occupies a large amount of radio spectrum. The noise-induced error in this timing synchronization tends to accumulate and propagate from upper hierarchical reference transmitters to lower hierarchical reference transmitters, thereby limiting the accuracy of the positioning function.
Golf course positioning systems by Huston et al (U.S. Pat. No. 5,364,093), Fraker et al (U.S. Pat. No. 5,434,789), and Boman (U.S. Pat. No. 5,469,175) incorporate a Global-Positioning System (GPS) receiver in a mobile unit to determine the golfer's location and the distance to the pin. The available accuracy of the (CA-code based) Global Positioning System is limited by the Selective Availability to 100 meters. To increase the accuracy of such systems, a fixed-location reference base station for determining the inaccuracy of the Global-Positioning System receiver and for periodically broadcasting differential-correction information to the mobile unit is installed on the golf course. Since the mobile unit of such differential GPS-based systems requires a GPS receiver and a separate receiver for receiving the differential correction in addition to a data processor, the hardware cost is quite high and hardware and the battery required can make such mobile unit quite heavy.
The system described in U.S. Pat. Nos. 5,526,357 and 5,365,516 issued to Jandrell uses time-division spread spectrum-signaling technique for communication and transponder locationing. The system contains a control center, an array of networked base stations, and a plurality of transponders. The system employs the hierarchical mater-slave synchronization technique in which the control center disseminates timing pulses for the synchronization of the time-bases of the networked base station. The base station then disseminates timing pulses to adjacent regions. Similar to the ranging and direction finding system by Wang et al, such network-wide time-base synchronization requires significant amount of bandwidth and the accuracy of the positioning is plagued with error propagation problems associated with the hierarchical master-slave timing synchronization system. In the CDMA communications and geolocationing system by Schilling (U.S. Pat. Nos. 5,365,544 and 5,506,864), the ranging between a plurality of base stations and remote units is achieved with a common type of echo ranging measurement method that is used in radar systems. The system determines the range between a base station and a remote unit, but not the position of the remote unit, or the distance to any of the pre-defined feature.
Therefore, none of the prior art systems listed on golf courses combine a position location system with voice or data communication capabilities. Conversely, the prior art spread spectrum communication systems would be difficult to use on a golf course.